Engine: api v2 root-node for single-object responses
Engine: API v2 - ping controller and /api/ping route
Engine: API v2 - fixing bad merge-conflict resolution

these files were moved:
app/views/api/v2/common/collection_resource.json.rabl --> app/views/katello/api/v2/common/collection_resource.json.rabl
app/views/api/v2/common/single_resource.json.rabl --> app/views/katello/api/v2/common/single_resource.json.rabl